1. Field of the Invention
The present invention is directed to an improved extracorporeal conduit and methods and systems for deriving desired biologic constituent concentration values present in a flowing fluid.
2. Background
Medical professionals routinely desire to know the hematocrit, oxygen saturation, and oxygen consumption rate of a patient. Especially in critically ill patients or in cardiovascular surgery, the oxygen consumption rate, hematocrit value and microemboli content become very significant parameters.
The prior art contains disclosures of flow-through cuvettes that may be used in a blood conduit for the spectrophotometric analysis of blood. For example, U.S. Pat. No. 5,456,253 discloses a disposable conduit/cuvette for analyzing blood.
It is an object of the present invention to provide systems and methods for noninvasively and continuously monitoring such biologic constituents as the percent blood volume change, hematocrit, oxygen saturation, oxygen consumption rate, and microemboli content during such treatment/procedures as hemodialysis or cardiovascular surgery.
It is another object of the present invention to monitor the above mentioned parameters without incurring instabilities, inaccuracies, and the need for recalibration as required in the presently known reflective and transmissive photometric techniques.
Another object of the present invention is to measure hematocrit, blood volume, oxygen saturation, oxygen consumption rate, microemboli, and cardiac output and visually display their corresponding values in real-time.
It is still another object of the present invention to provide systems and methods that are easy to use, save nursing staff time, and operate noninvasively and economically.
Another object of the present invention is to provide a cuvette which may be used in spectrophotometric determinations of desired biologic constituent concentration values of a fluid passing through this cuvette accommodating a large range of flow rates.
Another object of the present invention is to provide in this fluid-channeling cuvette a means by which the detection of the above mentioned parameters are unaffected by large variations in flow rates and are likewise unaffected by large variations in oxygen saturation such that the computation of blood constituent and blood flow parameters, including cardiac output, may be easily accomplished.
It is a further object of the present invention to provide a flow-through cuvette having a fixed, small path length.
These and other objects are achieved by the methods and apparati of the present invention.
The present invention provides a cuvette having a pedestal for transmitting light through a relatively thin layer of blood. While the pedestal enables the use of a small path length it also permits the use of a high volume and/or high flow rate conduit. Because the pedestal is situated within a large volume cuvette, the blood pressure within the cuvette remains low. The pedestal further enables methods of determining various blood parameters in which the path length, d, is fixed; i.e., there are little or no pulsatile variations.
The ability to change the internal and external dimensions of the blood chamber to accommodate for very large blood flows is important, especially with flow rates of 100 ml/min to 7,000 ml/min used in cardiovascular surgery. Hence, the flow-through cuvette of the present invention accommodates a large range of blood flow rates without any reduction in accuracy of the hematocrit measurement. The pedestal in the cuvette of the present invention because of its elliptical shape does not damage or hemolyze the individual red blood cells as they pass through.
The present invention further provides a quantitative method for determining changes in blood volume in view of the path length.
The present invention also provides a method for measuring a patient""s cardiac output and oxygen consumption rate. Cardiac output is obtained by injecting a saline arterial bolus and a saline venous bolus into a patient and measuring the change in hematocrit caused by each bolus. The oxygen consumption rate is then determined using the cardiac output and measuring the degree of oxygen saturation.
The present invention further provides an improved cuvette and corresponding method of measuring microemboli. The cuvette contains multiple mini-lenses that focus narrow beams of light through the blood. These narrow beams of light are individually monitored by detectors. When a microemboli, such as platelet aggregates, clots, air bubbles, etc. pass through a beam, a xe2x80x9cspikexe2x80x9d is recorded by a detector. The amplitude and width of spikes provides information on the size of microemboli and the spike frequency provides information on the concentration of microemboli.